Super cooler for a heat producing device

ABSTRACT

A super cooler device including a thermo electric cooler on a digital micro mirror device.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims benefit of U.S. ProvisionalApplication No. 60/181,530 filed Feb. 10, 2000.

[0002] The present application relates to cooling of a heat producingdevice, using a thermoelectric cooler arranged as a super cooler. Morespecifically, the present application teaches cooling of a device, suchas a digital mirror device, which requires a specified temperaturegradient across the device, using a supercooled element.

BACKGROUND

[0003] Electronic devices often have specified cooling requirements. Onedevice that has specific cooling requirements is a digital micromirrordevice (“DMD”) available from Texas Instruments (“TI”). The manufacturerof this device has specified a maximum overall temperature for thedevice and also a specified maximum temperature gradient between thefront and rear faces of the device during operation.

[0004] For example, the temperature of the specific DMD used in thisapplication needs to be kept below 55° C., however, in this applicationit is desirable to keep the device at or below ambient. This may allowoperation in an ambient environment up to 55° C., such as may beencountered in a stage theater or studio environment. The temperaturedifferential between the front and rear of the DMD cannot exceed 15°.Besides the heat from the operation of the DMD itself, large amounts ofheat from a high intensity light source must be dissipated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] These and other aspects will now be described in detail withreference to the accompanying, wherein:

[0006]FIG. 1 shows an exploded diagram of the parts making up thesupercooler assembly;

[0007]FIG. 2 shows the rear of the DMD and parts which are assembled tothe DMD;

[0008]FIG. 3 shows a circuit for driving a thermoelectric cooler; and

[0009]FIG. 4 shows a flowchart of operation.

DETAILED DESCRIPTION

[0010] According to the present system, a “supercooler” device, is usedto monitor and control the temperature of a device which can controllight on a pixel-by-pixel basis, e.g. a digital mirror device (DMD).

[0011] The mechanical structure of the supercooling assembly is shown inFIG. 1. The pixel element is a DMD 99, which forms part of a DMDassembly 100. As shown, a thermal connection 105 to the DMD 99 isprovided.

[0012] A cold plate 120 is assembled to a mounting bracket 110 in amanner which allows minimal thermal transfer between the two components.The DMD is attached directly to the cold plate 120, hereby allowingmaximum thermal transfer between the DMD and cold plate 120, but minimalthermal transfer to the mounting bracket 110. The rear surface of thecold plate 120 is directly connected to one side of the thermoelectricdevice 130, and the other side of the thermoelectric device is connectedto a heat sink/fan assembly 140.

[0013] Insulating foam gaskets are fitted around the DMD rear stud, thecold plate, and the thermoelectric device in order to isolate them fromthe outside ambient air. This improves the efficiency of the coolingsystem by eliminating the effects of condensation and properlycontrolling the flow of heat from the DMD to the cold plate, through thethermoelectric device, and into the heat sink/fan assembly.

[0014] The thermoelectric cooler element 130 operates as conventional toproduce one cold side 131 and one hot side 132. The hot side is coupledto the heat sink/fan assembly 140 to dissipate the heat. In a preferredmode, the heat sink/fan assembly is columnar is shape, with asubstantially square cross section. This facilitates using a squareshaped fan housing 142. The square shaped fan unit allows the maximumuse of the space for a fan, whose blades usually follow a round shape.Any type of cooling fan, however can be used.

[0015] The DMD assembly 100 has an extending rear stud 105 which iscovered with thermal grease. This stud extends though a hole 112 in thebracket assembly 110.

[0016] The plate 120 is actively cooled, and hence becomes a “coldplate”. The active cooling keeps the metal plate at a cooledtemperature, and the thermal characteristics of the plate material allowthe heat flowing into the plate from the DMD to be evenly distributedthroughout the entire plate. The plate is preferably about ¼″ to ⅜″ inthickness, and of comparable outer size to the thermal contact area ofthe thermoelectric cooler element 130. This allows the localized andconcentrated heat at the rear stud of the DMD to be evenly dissipatedthrough the cold plate and then efficiently transferred through the fullsurface area of the thermoelectric cooler element. As shown, theassembly employs thermal insulation techniques such as fiber/plasticsleeves and washers in the mounting of components, in order to preventheat transfer via mounting screws etc. Since this heat transfer could beuncontrolled, it could otherwise reduce the cooling efficiency.

[0017] The front of the DMD is shown in FIG. 2. Temperature sensor 200is mounted to have a fast response to temperature changes. A secondtemperature sensor 122 is mounted to the cold plate 120 and effectivelymeasures the temperature of the rear of the DMD 99. This secondtemperature sensor 122 therefore monitors the back temperature.

[0018] The hot side 132 of the thermoelectric cooler is coupled to aheat sink assembly 130. The heat sink assembly 140 includes a heat sinkelement 140. As shown, the device has fins and a top-located cooling fan142.

[0019] A block diagram of the control system is shown in FIG. 3.Controller 300 operates in a closed loop mode to maintain a desiredtemperature differential across the sensors 122, 200.

[0020] One important feature of the present application is that thethermoelectric cooler is controlled to maintain the temperature of theDMD at the desired limits. These limits are set at a target of 16° C. onthe front, and a differential no greater than 15° between front andrear. The thermoelectric cooler is controlled using very low frequencyor filtered pulse width modulation. In a first embodiment, thecontrolling micro controller 300 produces an output 302, e.g., digitalor analog. This drives a pulse width modulator 304. The output of thepulse width modulator is a square wave 306 or a signal close to a squarewave, with sufficient amplitude and power to produce the desired levelof cooling down the thermoelectric cooler. The square wave is coupled toan LC filter 308 which has a time constant effective to smooth the 20KHz switching frequency. The output to the thermoelectric cooler istherefore a DC signal. This drives the thermoelectric cooler 130 andcauses it to produce a cooling output. In a second embodiment, the LCfilter is removed and the TEC is driven directly by the square wave 306at a lower frequency, e.g. 1 Hz.

[0021] The microcontroller operates according to the flowchart of FIG.4. Step 400 determines if the temperature of the first temperaturesensor T1 is greater than 16°. If so, the output to the TEC remains“on”, resulting in further cooling. When the temperature falls below16°, the drive to the TEC is switched off. The sample period isapproximately ½ second between samples.

[0022] At 410, the system checks temperature of the first sensor (T1)and of the second sensor (T2) to determine if the differential isgreater than 15°. If so, the output is switched “on”. Step 420 indicatesa limit alarm, which represents the time of increase if the rate ofchange continues. If the rate of change continues to increase, asdetected at step 420, a fault is declared at step 425. This fault cancause, for example, the entire unit to be shut off, to reduce the powerand prevent permanent damage.

[0023] Other embodiments are contemplated.

What is claimed:
 1. An apparatus, comprising: a temperature sensingdevice, monitoring a front temperature of a front surface of a firstdriven device, and a rear temperature related to a rear surface of thefirst driven device; a controller, detecting both a temperature of thefirst driven device and a temperature differential across the firstdriven device; a thermoelectric cooler, coupled to actively cool thefirst driven device under control of said controller; and wherein saidcontroller produces outputs which control both overall temperature ofthe first driven device and temperature differential of the first drivendevice.
 2. An apparatus as in claim 1 , wherein the first driven deviceis a digital mirror device.
 3. An apparatus as in claim 1 , furthercomprising a lighting projector, projecting light on said front surfaceof said first driven device.
 4. An apparatus as in claim 1 , furthercomprising a pulse width modulated device, driven by said controller, toproduce a pulse width modulated output to drive said thermoelectriccooler.
 5. An apparatus as in claim 4 , wherein said pulse widthmodulated output is applied directly to said thermoelectric cooler. 6.An apparatus as in claim 4 , further comprising a filter, which filterssaid pulse width modulated output, to provide a smoothed output.
 7. Anapparatus as in claim 1 , further comprising a super cooler assembly,connected to a hot side of said thermoelectric cooler, said super coolerassembly including a metal plate, a heat sink, connected to said metalplate, and a fan, actively cooling said heat sink.
 8. An apparatus as inclaim 7 , wherein said temperature sensing device includes a sensormounted to said metal plate.
 9. An apparatus as in claim 7 , furthercomprising insulation, mounted to insulate portions of said first drivendevice, to insulate said first driven device from ambient.
 10. Anapparatus as in claim 9 , wherein said first driven device is a digitalmirror device.
 11. An apparatus as in claim 7 , wherein said heat sinkhas a cross-sectional area which is substantially square, and an outerframe of said fan is substantially square and coupled to said heat sink.12. An apparatus as in claim 11 , wherein said heat sink has a squarecross-section, in a first direction, and has a rectangular cross-sectionin a second direction.
 13. An apparatus as in claim 6 , wherein saidfilter includes an LC filter.
 14. An apparatus as in claim 1 , whereinsaid controller monitors overall temperature of the first driven device,a ratio between front and rear temperature of the first driven device,and an increment over time of cooling of the first driven device.
 15. Anapparatus as in claim 14 , wherein the first driven device is a digitalmirror device.
 16. An apparatus as in claim 2 , further comprisinginsulation between said digital mirror device and ambient.
 17. Anapparatus, comprising: a digital micro mirror device assembly, includinga mounting plate for a digital micro mirror device, and a digital micromirror device mounted on said mounting plate; and insulation, positionedaround at least a part of said digital micro mirror device, to insulatesaid at least part of the digital micro mirror device from ambient. 18.An apparatus as in claim 17 , further comprising a thermoelectriccooling device, coupled to cool said at least part of the digital micromirror device.
 19. An apparatus as in claim 18 , further comprising acontroller for said thermoelectric cooling device.
 20. An apparatus asin claim 19 , further comprising temperature sensors on said digitalmicro mirror device, wherein said controller is operative responsive tosaid temperature sensors, to control at least one temperature of saiddigital micro mirror device.
 21. An apparatus as in claim 20 , whereinsaid controller controls production of a pulse width modulated signal,whose pulse width is based on said temperature.
 22. An apparatus,comprising: a digital micro mirror device assembly, including a digitalmicro mirror device mounted thereon; and an active cooling unit, coupledto cool said digital micro mirror device.
 23. An apparatus as in claim22 , wherein said active cooling unit includes a thermoelectric cooler.24. An apparatus as in claim 23 , further comprising a temperaturesensor, sensing a temperature of said digital micro mirror device, and acontroller, controlling said thermoelectric cooler based on the sensedtemperature.
 25. An apparatus as in claim 24 , wherein said temperaturesensor includes a first temperature sensor sensing a temperature nearthe front of the digital micro mirror device, and a second temperaturesensor sensing a temperature near the rear of the digital micro mirrordevice.
 26. An apparatus as in claim 25 , wherein said controlleroperates to control the thermoelectric cooler based on both the fronttemperature, and a difference between the front and rear temperatures.27. An apparatus as in claim 22 , further comprising a controller forsaid active cooling unit, said controller controlling production of apulse width modulated signal that controls the active cooling unit. 28.An apparatus as in claim 26 , further comprising a controller for saidactive cooling unit, said controller controlling production of a pulsewidth modulated signal that controls the active cooling unit.
 29. Anapparatus as in claim the 28, further comprising a filter which smoothssaid pulse width modulated signal to reduce an amount of transitionstherein.
 30. An apparatus as in claim 29 , wherein said filter includesan LC filter.
 31. An apparatus as in claim 22 , further comprising aplate formed of heat distributing material, coupled to said digitalmicro mirror device assembly and said active cooling unit, and of a sizewhich is affective to evenly distribute heat from the digital micromirror device assembly into said plate.
 32. An apparatus as in claim 31, further comprising a temperature sensor, sensing a temperature of saiddigital micro mirror device, and a controller, controlling saidthermoelectric cooler based on the sensed temperature.
 33. An apparatusas in claim 32 , wherein said temperature sensor includes a firsttemperature sensor, sensing a temperature near a front of the digitalmicro mirror device, and a second temperature sensor sensing atemperature of said plate, and wherein said controller operates both onsaid front temperature, and based on a difference between said front andsaid rear temperature.
 34. As apparatus in claim 22 , further comprisinginsulation coupled between said digital micro mirror device and ambient,to insulate said digital micro mirror device from ambient.
 35. Anapparatus as in claim 31 , further comprising a heat sink and fan,connected to said plate, to dissipate heat from said plate.
 36. Amethod, comprising: operating a digital micro mirror device in anenvironment where one side thereof is exposed to heat from light that isapplied thereto; and actively cooling the other side of said digitalmicro mirror device.
 37. A method as in claim 36 , wherein said activelycooling comprises using a thermoelectric cooler coupled to an other sideof said digital micro mirror device.
 38. A method as in claim 36 ,wherein said actively cooling comprises using a pulse width modulatedsignal to control an amount of cooling provided by said thermoelectriccooler.
 39. A method as in claim 38 , further comprising filtering saidpulse width modulated signal prior to applying said signal to saidthermoelectric cooler.
 40. A method as in claim 36 , further comprisingdetecting a temperature of said digital micro mirror device, and whereinan amount of said active cooling is based on the detected temperature.41. A method as in claim 40 , wherein said detecting comprises detectinga temperature of the front of the digital micro mirror device and atemperature of the rear of the digital micro mirror device.
 42. A methodas in claim 41 , wherein said amount of active cooling is based both ona temperature of the front of the device and on a differential betweenthe temperature of the front of the device and a temperature of the rearof the device.
 43. A method as in claim 36 , further comprising:detecting a temperature of the digital micro mirror device; detecting atemperature near a rear of the digital micro mirror device; determininga temperature of the digital micro mirror device, and a differencebetween a temperature of the micro mirror device and a rear temperatureof the micro mirror device, and changing a cooling amount based on bothsaid temperature and said difference.
 44. A method as in claim 43 ,further comprising determining a rate of change of increment oftemperature, and establishing a fault if said rate of change is higherthan a specified amount.
 45. A method as in claim 36 , furthercomprising insulating the digital micro mirror device from ambienttemperature.
 46. A method, comprising: energizing a digital micro mirrordevice; determining a first temperature related to a front of thedigital micro mirror device and a second temperature related to a reartemperature of the digital micro mirror device; forming a pulse widthmodulated control signal based on both temperature on the front of thedigital micro mirror device, and a difference between temperature of thefront and rear of the digital micro mirror device; and actively coolingthe rear of the digital micro mirror device based on said pulse widthmodulated signal.
 47. A method as in claim 46 , further comprisingfiltering said pulse width modulated signal, prior to said activelycooling.
 48. A method as in claim 46 , further comprising insulatingsaid digital micro mirror device from ambient temperature.
 49. A methodas in claim 46 , further comprising dissipating heat from the activelycooling using a heat sink and fan.
 50. A method as in claim 46 , whereinsaid forming comprises establishing a desired temperature and a desiredtemperature differential, and increasing and active amount of said pulsewidth modulated signal when said desired temperature is exceeded, anddecreasing said active amount when said desired temperature differentialis exceeded.